Entries in this blog

[b]Previous update[/b]
[color=#282828][font=helvetica, arial, sans-serif]I expect the continuation of unsettled conditions, with on average temperatures remaining close to the norm. Given the expected continuation of a â€“NAO, and â€“AO I would not bet against colder interludes, in the form of brief northerlys, as we progress through the xmas period (something which has shown around xmas day on the latest model runs). I do not see great support for something prolonged this side of New Year. Given developments in the stratosphere I think the first half January, probably past week one, is when it could potentially come very interesting..![/font][/color]

[b]Review[/b]
[color=#282828][font=helvetica, arial, sans-serif]It remained unsettled and mostly average, although cooler at times further north. Although the NAO and AO remained negative, they have now trended towards positive, and likely to be so as we start January. Something hinted by the ensemble forecasts in my last update. Those 'interesting developments in stratosphere' seem likely to develop, although as highlighted in the last update, no impact on us is expected by week one. The initial forecast went bust, however the update has got relatively better, although perhaps milder than i expected.[/font][/color]

[b]Stratospheric outlook[/b]
[color=#282828][font=helvetica, arial, sans-serif]After a period of temperatures at just below average at 10hpa, and recently just above at 30hpa, a large spike at all levels is expected as we progress into January.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150342"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-07620200-1356787986_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150343"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-59528500-1356787987_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150353"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-89853500-1356788018_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150352"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-52127700-1356788017_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Stratospheric temperatures at the 10hpa and 30hpa level are to increase significantly during the New Year period. The strength of the warming should lead to significant disruption of the polar vortex, and thus high latitude blocking.[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]Mean zonal winds are expected to decrease, reversing at 30hpa, and then most probably at 10hpa. Although not a sudden stratospheric warming (yet), I would expect this to be shown soon (zonal wind reversal at the 10hpa). Again, this should lead to significant disruption of the polar vortex.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150345"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-42468800-1356787990_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150346"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-67200500-1356787991_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]Split or displacement? I would probably suggest a displacement followed by a possible split. Wave one breaking is expected to increase significantly, before decreasing at the end of the forecast period. Wave one breaking is characterised with vortex displacement.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150344"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-18309800-1356787989_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150339"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-37589200-1356787979_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Interestingly, wave two breaking is forecast to increase, which favours vortex split.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150365"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-70651100-1356788061_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]It is difficult to predict the area where the displaced vortex is likely to locate. At the moment I would suggest our side of the Atlantic (west Greenland area), which is not favourable for us. However, there are hints from the longer range GFS that subsequent warming nearer midmonth (Greenland area) may change this situation![/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150348"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-59555900-1356788005_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150368"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-93610100-1356788246_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]MJO[/b]
[color=#282828][font=helvetica, arial, sans-serif]A mixed output from the global models, although all indicate an increasing amplitude. The UKMO is by far the most interesting, and has for some time indicated a possible phase 7/8 by midmonth. The ECM is similar to the UKMO, although slower with its evolution. The GFS seems to be on its own, although the bias corrected ensembles seem to follow the euros, albeit slower.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150364"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-51889800-1356788042_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150347"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-93694800-1356788003_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150363"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-16826000-1356788042_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Some not so good phases to get through beforehand, which in general indicate lower heights to our north, with higher pressure progressively shifting north, so becoming settled.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150357"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-74529300-1356788037_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150358"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-76363400-1356788038_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150359"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-81589200-1356788039_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Phase 7/8 would support height rises towards Greenland, around or just past midmonth (based on the UKMO/ECM).[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150360"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-41577800-1356788040_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150361"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-99721700-1356788040_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]The GWO has progressed towards phase 4, with a corresponding increase in angular momentum. From reading a few papers I noted how this is associated with a higher amplitude and progression of the MJO, which is ideal for a progression towards phase 7/8. Although given my relatively basic understanding of atmospheric angular momentum (first year uni) I shall not delve on this topic.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150355"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-00013000-1356788021_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150337"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-87940800-1356787975_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Interestingly the following composites show a GWO phase 5/6/7/8 is associated with below average UK temperatures.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150356"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-62348500-1356788036_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]CFS charts[/b]
[color=#282828][font=helvetica, arial, sans-serif]Although not the most reliable charts, the general trend for weeks one-two is for lower heights to our north, with higher heights to our south (+NAO). With a trend for these higher heights to push further north (i.e. the UK becoming settled at last).[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Past midmonth there is a signal for height rises over Greenland, with uncertainties in the placement of the trough.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150366"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-99912600-1356788062_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150367"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-36115900-1356788064_thumb.gif[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]AO and NAO Ensembles[/b]
[color=#282828][font=helvetica, arial, sans-serif]The ensembles continue to show +NAO and +AO as we beguine the new year. However, there are some indications from the GFS that the AO shall return negative towards mid-month, which is expected.[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150350"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-25846400-1356788012_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]The NAO forecasts are rather disappointing, and show a +NAO towards mid-month[/font][/color]
[url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150351"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-65644400-1356788016_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][url="http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=150341"][img]http://forum.nwstatic.co.uk/uploads/monthly_12_2012/post-6181-0-00728600-1356787984_thumb.png[/img][/url][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]

[b]Overall[/b]
[color=#282828][font=helvetica, arial, sans-serif]An unsettled start to the month, but becoming progressively drier as higher pressure attempts to progress north east. Thereafter potentially becoming unsettled again. Midmonth I expect a change towards much colder conditions, with height rises in the Greenland region (around day 15 ish). I expect colder conditions, if they materialise, to be relatively sustained. In summary, a mild start (cooler when settled), and a cold end.[/font][/color]

Overall im finding it rather difficult to produce a forecast, but then isnâ€™t it always! Whatâ€™s apparent is the PV shall remain disrupted and disorganised as we progress through December. I am generally supportive of height rises to the NE given the latest runs, although feel that these will transfer nearer Greenland as we progress through the month when we see further wave breaking disrupting the vortex and leading to more movement of the PV segments. This would also be supported by the GFS MJO outlook, and ensemble forecasts for the NAO from both the ECM and GFS. The CFS could also be included. Weatherwise a cold and unsettled start, with the potential for height rises to out NE, and some sort of easterly flow during the first third. As we progress into midmonth and beyond I feel higher pressure would transfer closer to Greenland, bringing a more N/NEâ€™rly flow.

[b]Review so far[/b]

The month started on a cold and unsettled note, while expected height rises to the north east materialised. Unfortunately we did not see the easterly flow that i expected, with low pressure from the west taking control, introducing unsettled weather with temperatures close to the average. Despite this the PV has remained disrupted, with a -AO and -NAO which has prevented us from experiencing something from winters past (i.e. Bartlett type weather). Itâ€™s apparent that my forecast of midmonth height rises over Greenland via retrogression from scandi will not materialise, and thus a north/north east flow.

[b]Update and initial January thoughts[/b]

The following update and forecast is based on the latest stratospheric output, MJO, CFS, AO and NAO ensemble means, as well as 500hpa and 850hpa means.

[b]Stratospheric outlook[/b]

[font="helvetica, arial, sans-serif"][color="#282828"]Stratospheric temperatures at the 10hpa and 30hpa level are running just below the average, and have done since a small warming event at the beginning of the month. They are forecast to remain just below average for the next 10 days, with temperatures rising at 30hpa by day 10 (as shown on the ECM temperature charts). Note i have used the graphs for simplicity.[/color][/font]
[attachment=149126:temp graphs.gif]
[color=#282828][font=helvetica, arial, sans-serif]Although not as apparent on the temperature graph, a major warming at the 10hpa level is forecast from day ten onwards (Siberian sector), this is shown the ECM 10hpa geopotential height charts at day and ten, and the GFS strat charts.[/font][/color]
[attachment=149116:ECM t240 10hpa.gif][attachment=149130:gfs_t10_nh_f240.gif]
[color=#282828][font=helvetica, arial, sans-serif]The most significant warming is still out of range for above charts, however the GFS 12z strat charts show this nicely, and have done for some time (and are not pushing back)[/font][/color]
[attachment=149123:gfsnh-10-348.png]
I suspect this will lead to major disruption of the PV, or the killer blow seen as its not exactly rampant at present. This would be expected as we progress into January. For the rest of December, I expect the continuation of the relatively weak PV, centred towards the Siberia, which opens up potential for height rises over Greenland.
[attachment=149113:ECM geo t240.gif]
Zonal winds have risen slightly since a drop at the beginning of December, and are forecast to decrease again. Given their current and predicated strength I would expect the continuation of a weak(ish) PV.
[attachment=149124:graphs zonal.gif]
Further wave breaking is forecast by day ten, most notable wave one. This should displace the PV, and further stress it. It is also noted that wave two activity shows signs of increasing, which would place even greater stress on already strained PV.
[attachment=149128:wave one.gif][attachment=149129:wave two.gif]

[b]MJO outlook[/b]

There seems consensus to progress the MJO into phase two, although not of high amplitude.
[attachment=149119:GFS mjo.gif][attachment=149114:ECM mjo.gif][attachment=149127:UKMO mjo.gif]
The UKMO is interesting in that wants to progress the MJO through higher amplitude phase one beforehand, which would give the following composite which has height rises over Greenland and a trough over the UK (although bear in mind these are to be used as guides).
[attachment=149111:DecemberPhase1500mb.gif]
The composite for phase two MJO is the following
A trough with the core of lower heights situated over the UK (i.e. unsettled)
[attachment=149112:DecemberPhase2500mb.gif]

[b]CFS charts[/b]
[color=#282828][font=helvetica, arial, sans-serif]Weeks one and two show a trough situated in the Atlantic, unfavourably for us, leading to unsettled and probably mild (at times), weather. Looking at all forecasts from Sunday 9[/font][/color][sup]th[/sup][color=#282828][font=helvetica, arial, sans-serif] there seems a trend for height anomalies to continue above the norm around Greenland as progress past xmas day and into new year, with the core of lower heights transferring from the Atlantic into Europe. This would open the door to something a little more seasonal (e.g. northerly airstream).[/font][/color]
[attachment=149110:CFS week one-two.gif][attachment=149131:weeks three-four.gif]

[b]AO and NAO Ensembles[/b]

The ensembles support the continuation of a â€“AO, although trending towards positive as we move towards months end and then negative again.
[attachment=149118:GFS AO.png]
Further to this there is support for the continuation of a mostly â€“NAO, although trending towards positive for months end.
[attachment=149120:GFS NAO.png][attachment=149115:ECM NAO.png]

[b]Mean height ensembles[/b]

The ECM ensemble mean supports the continuation of higher pressure to the north (Greenland area) and the core of lower heights in the Atlantic, with the continuation of unsettled weather.
[attachment=149117:ECMWFENS6-10day500mbHeightAnomalyNH.gif]
Analysis of the 850hpa anomalies would indicate that temperatures should remain close to average, despite being unsettled.
[attachment=149108:00zecmwfenshourly850mbTempAnomalyNH216.gif][attachment=149109:00zecmwfenshourly850mbTempAnomalyNH240.gif]
The GFS is similar, although perhaps more interesting by day ten to fifteen, with the core of lower heights into Europe and indication that UK might experience something a little more seasonal (i.e. some sort of northerly) past xmas day.
[attachment=149121:GFS6-10day500mbHeightAnomaly.gif][attachment=149122:GFS11-15day500mbHeightAnomalyNH.gif]
This is also supported by the NAEFS
[attachment=149125:naefs-0-0-360.png]

[b]Overall[/b]

I expect the continuation of unsettled conditions, with on average temperatures remaining close to the norm. Given the expected continuation of a â€“NAO, and â€“AO I would not bet against colder interludes, in the form of brief northerlys, as we progress through the xmas period (something which has shown around xmas day on the latest model runs). I do not see great support for something prolonged this side of New Year. Given developments in the stratosphere I think the first half January, probably past week one, is when it could potentially come very interesting..!

[b]December outlook [/b]
The following forecast is based on the latest stratospheric output, MJO, CFS, AO and NAO ensembles means, as well as 500hpa and 850hpa means.

[b]Stratospheric outlook[/b]

Stratospheric temperatures at both the 10hpa and 30hpa level are set to increase, as shown on the following diagrams. This should strain the vortex and encourage blocking.
[attachment=146385:ECM current temp. conditions.gif][attachment=146388:ECM T240 temp. conditions.gif]
The GFS also indicates a warming event. I note how the warming on the pacific side is extending into North America, pushing the coldest temperatures to the East of Greenland. This would support a large segment of the PV shifting into this region later in December, and lend support to a -NAO. It is important to note however that the troposphere and Stratosphere interactions seem to have been different this year, which would cast some doubt on this assumption. The extended cool period and higher zonal winds did not lead to strong and organised PV that some may have expected as we progressed through November. Why this occurred is beyond my knowledge.
[attachment=146408:Warming forecast current GFS.gif][attachment=146409:Warming forecast T240 30hpa.gif]
Mean zonal temperatures are forecast to decrease which again would strain the vortex and encourage blocking
[attachment=146386:ECM current zonal conditions.gif][attachment=146389:ECM T240 zonal conditions.gif]
I have limited understanding of waving breaking. I believe it stands for reflection of large-scale planetary waves off mountain chains that break into stratosphere, which in turn places pressure onto the vortex. If we use CHâ€™s analogy of the balloon then it is perhaps simpler to understand how two wave breaks in the NH (placing pressure on two points of the vortex) can lead a split vortex, while one wave break (placing pressure at one point of the vortex) can lead to disruption,
We can see from the ECM forecast that wave two activity is set to peak over the next few days, before petering out.
[attachment=146390:ECM wave break T144 (2).gif][attachment=146392:ECM wave break T240 (2).gif]
However, wave one is forecast to increase substantially at the day ten. So using the CHâ€™s analogy, this should lead to further disruption (of an already disorganised) PV.
[attachment=146391:ECM wave break T240 (1).gif]
I should probably pass over the wave breaking section, Iâ€™ve only included it with the hope that one of the experts may correct me if any of my interpretation is wrong.

The latest ECM geopotential height charts support higher pressure in the mid-atlantic with a NW west flow, as does the GFS. Based on these charts I would suggest height rises over Greenland are some way off (i.e. past day ten).
[attachment=146393:Geo height 100hpa t240.gif][attachment=146398:GFS t240 geo height.gif]

[b]MJO outlook [/b]

The MJO signal is weak, with most models indicating that will remain in low amplitude. The UKMO seem keen on a weak phase one or two, the ECM on a weak phase one or eight while the GFS predicts a higher amplitude phase one (although briefly skirting through phase eight). Based on the forecasts I would have probably discounted the MJO. The GFS however has been keen on a higher amplitude phase one, and has for some days. The ECM would support phase one, albeit in much lower amplitude.
[attachment=146407:UKMO MJO phase forecast.gif][attachment=146387:ECM MJO phase forecast.gif][attachment=146396:GFS MJO.gif]
Phase one MJO would give us the following composite, heights over Greenland, and a trough over the UK. Note that these composites should only be used as a guide.
[attachment=146383:DecemberPhase1500mb.gif]

[b]CFS charts[/b]

Not a model I normally use however the trend has been for higher heights in the mid-Atlantic and over Siberia for weeks one-two, with some support for higher pressure in these regions for weeks three-four. I should note there has been variability in these runs over the past week, although there is a theme for higher heights in the said areas.
[attachment=146381:CFS outlook week 1-2.gif][attachment=146382:CFS outlook week 2-4.gif]
The monthly CFS, for some time now, has indicated a below average December, with considerable blocking to our North.
[attachment=146380:CFS heights forecast december.gif][attachment=146379:CFS global temp forecast december.gif]

[b]AO and NAO Ensembles[/b]

Both the GFS and ECM ensembles support a â€“NAO, after brief close to/positive spell, as we progress into and past the middle of December.
[attachment=146384:ECM AO outlook.png][attachment=146397:GFS NAO forecast.png]
The GFS also supports the general continuation of a -AO
[attachment=146395:GFS AO Forecasrs.png]

[b]Mean height ensembles[/b]

The ECM ensembles are supportive of higher pressure in the mid-Atlantic, and over the Scandinavian region, lending support to some sort of easterly by day ten.
[attachment=146399:Mean ECM T240.gif]
The ECM 850hpa mean temperatures are shown to be below average.
[attachment=146402:mean t850 ecm T240.gif]
The GFS ensemble mean is also supportive showing higher pressure in the mid-atlantic retrogressing northeast.
[attachment=146400:Mean height anoms t180.gif][attachment=146401:Mean height anoms t364.gif] [attachment=146404:Mean t850 t384.gif]
Which is also supported by the NAEFS and NOAA
[attachment=146405:NAEFS T198.png][attachment=146406:NAFES T364.png][attachment=146394:GEO height outlook next two weeks.gif]

[b]Overall[/b]

Overall im finding it rather difficult to produce a forecast, but then isnâ€™t it always! Whatâ€™s apparent is the PV shall remain disrupted and disorganised as we progress through December. I am generally supportive of height rises to the NE given the latest runs, although feel that these will transfer nearer Greenland as we progress through the month when we see further wave breaking disrupting the vortex and leading to more movement of the PV segments. This would also be supported by the GFS MJO outlook, and ensemble forecasts for the NAO from both the ECM and GFS. The CFS could also be included. Weatherwise a cold and unsettled start, with the potential for height rises to out NE, and some sort of easterly flow during the first third. As we progress into midmonth and beyond I feel higher pressure would transfer closer to Greenland, bringing a more N/NEâ€™rly flow.
I intend to update midmonth.

[b]Note: Next update either on Thursday or Sunday/Monday. All images below will/have change/d as they have only been hyper-linked, will attach them on the next update [/b]

Thought it would be fun to have a go at a little longer range forecasting. I am by no means expert, however have learnt bits and bobs over last few years of my net-weather membership!

I shall be basing my thoughts on the stratospheric output, MJO forecasts, long range ensemble forecasts and CFS weekly charts. Instead of writing a detailed explanation of how we interpret the stratospheric output, i shall instead refer you to the stratospheric thread in the winter section (see page one).

[b]Stratospheric output[/b]
(I made a recent post about this, so shall take it and adapt it a little)

A rather positive outlook, for those looking for blocking (and something cold). Mean zonal winds are set to decrease at both the 10hpa and 30hpa level, which will strain the polar vortex (PV), as evidenced by the geopotential height charts posted later.
[img]http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/fluxes.gif[/img]
A warming at the 30hpa is also predicted, taking it above average, with the 10hpa not to far behind. Again this will only place strain on the PV, leading to disruption and fragmentation (and a -AO)
[img]http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/temps.gif[/img]
[color=#282828][font=helvetica, arial, sans-serif]Looking at the geopotential height charts we see a split in the vortex by day 10 at the 100hpa[/font][/color]
[img]http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwf100f240.gif[/img]
[color=#282828][font=helvetica, arial, sans-serif]With sighs of splitting right up to the 10hpa level [/font][/color]
[img]http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwf10f240.gif[/img]
[font=helvetica, arial, sans-serif][color=#282828]The GFS forecasts are of a simualr nature to the ECM, with a split in the PV at the 100hpa, and splitting as far up as the 10hpa level[/color][/font]
[img]http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/gif_files/gfs_z100_nh_f240.gif[/img][img]http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/gif_files/gfs_z10_nh_f240.gif[/img]
[b][font=helvetica, arial, sans-serif][color=#282828]MJO outlook [/color][/font][/b]
[font=helvetica, arial, sans-serif][color=#282828]The ensemble forecasts for the MJO vary, the UKMO that was keen on a move to phase eight now suggests a low amplitude phase two, which suggests the following composite. Although given the low amplitude im uncertain what effect this would have. [/color][/font]
[font=helvetica, arial, sans-serif][color=#282828][img]http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/UKME_phase_23m_full.gif[/img][/color][/font]
[img]http://raleighwx.americanwx.com/MJO/DecemberPhase2500mb.gif[/img]
[font=helvetica, arial, sans-serif][color=#282828]The GFS seems determined to drive the MJO into a higher amplitude phase eight, then one. Which would suggest the following composite.[/color][/font]
[img]http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/NCPE_phase_21m_full.gif[/img][img]http://raleighwx.americanwx.com/MJO/DecemberPhase1500mb.gif[/img]
[font=helvetica, arial, sans-serif][color=#282828]The ECM wants to drive the MJO through low amplitude phase one, two and three. [/color][/font]
[img]http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ECMF_phase_51m_full.gif[/img]
[color=#282828][font=helvetica, arial, sans-serif]There seems great uncertainty in the MJO outlook, although on average from all the runs, i would probably suggest phase one seems more likely.[/font][/color]

[b][color=#282828][font=helvetica, arial, sans-serif]CFS weekly [/font][/color][/b]
[font=helvetica, arial, sans-serif][color=#282828]Not the most reliable charts but worth looking at none the less. Week one-two shows strong heights over Greenland, and lower heights to the south of us, which would lend support to a blocked and potentially cold start to December.[/color][/font]
[img]http://origin.cpc.ncep.noaa.gov/products/people/sweaver/cfs_fcst/images1/wk1.wk2_20121124.z500.gif[/img]
[font=helvetica, arial, sans-serif][color=#282828]Week three to four also shows heights over Greenland, but shows lower heights by the 2nd half of the month [/color][/font]
[img]http://origin.cpc.ncep.noaa.gov/products/people/sweaver/cfs_fcst/images1/wk3.wk4_20121124.z500.gif[/img]
[b][color=#282828][font=helvetica, arial, sans-serif]Ensemble[/font][/color]s [/b]
[font=helvetica, arial, sans-serif][color=#282828]Will update this later[/color][/font]

[font=helvetica, arial, sans-serif][color=#282828]Overall[/color][/font][color=#282828][font=helvetica, arial, sans-serif] [/font][/color]
Based on the output, i would suggest a blocked start to December, with the PV disrupted and fragmented (and a -AO)[color=#282828][font=helvetica, arial, sans-serif]. I also see support for height rises around Greenland. Despite the models chopping and changing on whether the coldest air will get us, i would suggest at some point, over the next few weeks, that there is a high chance it would. [/font][/color]